Printed circuits are widely used. Printed circuits typically are broadband in frequency and provide circuits that are compact and light. They are economical to produce and are common to many antenna applications. There are many different transmission lines generally used for microwave integrated circuits.
FIG. 1 is a cross-sectional diagram of a microstrip line 10, as is known in the prior art. The microstrip line 10 is a transmission line geometry with a single conductor trace 12 on one side of a dielectric substrate 14 and a single ground plane on the opposite side 16. Electromagnetic field lines 18 represent the electromagnetic field exists partly in the air above the dielectric substrate 14 and partly within the dielectric substrate 14 itself. Since it is an open structure, the microstrip line has a major fabrication advantage over stripline transmission lines or other transmission lines having a closed structure.
Microstrip lines typically have a characteristic line impedance range of 20 to 120 Ohms, which is calculated based on the width W of the single conductor trace 12 and the height H of the dielectric substrate 14 relative to the dielectric constant of the substrate material. FIG. 2 is a graph showing characteristic line impedance ranges for a range of W/H values and a range of dielectric constants. Often, multiple transmission lines need to be designed on a single dielectric substrate 14, which often means selecting a single substrate height with a specific dielectric constant for all transmission line needs. For matching purposes and other considerations, it is necessary and/or desirable to construct transmission lines having varying impedances on the selected single dielectric substrate. Therefore, the range of available characteristic line impedances is useful for flexibility in designing the transmission lines.
FIG. 3 is a cross-sectional diagram of a twin lead line 110, as is known in the prior art. The twin lead line 110 is a transmission line geometry with a top conductor trace 112 on one side of a dielectric substrate 114 and a bottom conductor trace 116 on the opposite side. The bottom conductor trace 116 has a width W similar to the width W of the top conductor trace 112. Electromagnetic field lines 118 represent the electromagnetic field exists partly in the air above the dielectric substrate 114 and partly within the dielectric substrate 114 itself. The twin lead line 110 is an open structure, similar to the microstrip line 10.
Twin lead lines 110 typically have a characteristic line impedance range of 40 to 100 Ohms, which is calculated based on the common width W of the single conductor trace 112 and the bottom conductor trace 116 and the height H of the dielectric substrate 114 relative to the dielectric constant of the substrate material. FIG. 4 is a graph showing characteristic line impedance ranges for a range of W/H values and an FR4 substrate. In antenna applications a twin lead line 110 may be desirable over a microstrip line 10 because it provides a balanced transmission line that is useful for feeding dipole elements. However, a drawback to the twin lead line 110 is a limited range of characteristic line impedances available for a single substrate thickness. As mentioned herein, a wide range of available characteristic line impedances is useful for flexibility in designing the transmission lines.
Twin leads may similarly be used for transmission line filters. Transmission line filters operate using impedance matching, as is known to those with ordinary skill in the art. Thus, having a wide range of available characteristic line impedances would be useful for flexibility in designing a transmission line filter.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.